Patent GB-183304-A (GB)
Abstract: 183,304. Automatic Telephone Manufacturing Co., Ltd., (Automatic Electric Co.). May 25, 1921. Automatic exchange systems and apparatus.- A branch exchange is provided with facilities for the transference of main exchange calls from one local subscriber to another without making any radical change in existing circuits or switches, any additional switches used being of common design. Two methods are described, the first as applied to a private branch exchange of 100 subscribers, in which a call from the main exchange to a P.B.X. subscriber A<1> is made over an incoming connector D, Fig. 1. at the P.B.X. If the subscriber A<1> wishes to transfer the call to a second local subscriber A<2>, Fig. 2, the first dials a prefatory digit 1 which causes a bridge to be placed across the line conductors of a repeater E, individual to the incoming connector D, thereby causing an associated line switch C, in which the trunks leading to the local connectors are multipled, to seize an idle local connector H, Fig. 2. The subscriber A' then dials the local number of the subscriber A<2>, interruptions in the bridge across the repeater E operating the local connector H, which extends the calling line to the local subscriber A<2>, the talking circuit including the line conductors of the repeater E and line switch C. The three subscribers may now converse over a three-cornered talking circuit. If the subscriber A' hangs up, the incoming connector D releases, and should the subscriber A<2> desire to transfer the call to a third local subscriber, the dialling of the prefatory digit 1 causes an operating circuit, extending from the repeater E, to be prepared for the previously-utilized incoming connector D. The subscriber A<2> now dials the number of the third local subscriber, successive de-energization of a line relay in the local connector H causing current reversals in the bridge across the repeater E, which completes the operating circuit of the incoming connector D, which in turn extends the calling line to the next wanted P.B.X. subscriber. The call may in this manner be transferred as often as desired, the incoming connector D and the local connector II being operated alternately. The second method is first described as applied to a 1000-line P.B.X. in which an incoming main exchange call is extended to a P.B.X. subscriber A, Fig. 4, over an incoming selector E<3>, Fig. 3, and an incoming connector H<3>, Fig. 4. To transfer the call the subscriber A dials a prefatory digit 1, as before, thereby causing a finder switch J, associated with the incoming selector E<3>, to set its wipers upon the same trunk as that engaged by the selector E<3>. The latter is then released, but the ca.ling line remains connected to the local subscriber A over the connector H<3> and the finder switch J. The subscriber A now dials the local number of the subscriber to whom it is desired to trarsfer the call, and the previously-used incoming selector E' is again operated to extend connection thereto over an idle incoming connector similar to H<3>. When the wanted subscriber answers, the finder J is restored and the transferring subscriber A automatically released, and if it is desired to transfer the call again, the connection to the second P.B.X. subscriber is extended over the finder J, and the incoming selector E<3> is used for establishing connection with a third P.B.X subscriber. The second method is also described as applied to a small P.B.X. of 100 lines, in which incoming connectors only are used. When a local subscriber desires to transfer a call, the calling line is side-tracked over a finder switch similar to J associated with the incoming connector, which is first released and subsequently again used to extend the calling line to another local subscriber. First method, Figs. 1 and 2. A main exchange call is extended to a P.B.X. subscriber A<1> in wellknown manner over the trunks 12, 13 and an incoming connector D. The usual back-bridge relay in the ccnnector D is omitted, but when the subscriber A<1> removes his receiver, an equivalent relay 101 in the associated repeater E is energized and a circuit is closed for a slow-release relay 102. If the subscriber A' desires to transfer the call to another local subscriber A<2>, when the prefatory digit 1 is dialled, the relay 101 is momentarily de-energized and a circuit is completed for a relay 103, which locks up over its armature 120 and prepares a bridge (112, 119, 106, 140) across the conductors 141, 142, which is closed when the relay 101 re-energizes a moment later. A circuit is thereby closed for the starting relay 151 of the associated line switch C, which operates in known manner to extend the repeater @IE to a trunk 166, 168 leading to an idle local connector H, the line relay 214 of which now responds and energizes the slow-release relay 215. The subscriber A<1> dials the local number of the wanted subscriber A<2>, the consequent de-energizations of the back-bridge relay 101 interrupting the bridge across the conductors 141, 142 and thereby de-energizing the line relay 214 of the local connector H, which operates in the usual manner to engage the wanted line A<2>. During the transmission of impulses a relay 100 is energized in a circuit 137, 117, 114, 132, closing a more direct bridge 112, 116, 111 across the conductors 141, 142, and shunting a resistance 144 across the calling line to prevent disagreeable dialling noises in the calling receiver. If the wanted local subscriber is busy, busy tone Q is transmitted to the main exchange subscriber and the local subscriber A<1>, and by hanging up his receiver for a short time the subscriber A' may open the bridge across conductors 141, 142, thereby de-energizing relays 214, 215 and closing a circuit for the release magnet 223 of the local connector H. Relay 215 also breaks the holding circuit of the line switch C which restores in known manner. If the subscriber A<2> is free. upon removing his receiver, talking current is supplied to him over a back-bridge relay 200, which reverses the current through the bridge across the repeater E, causing the response of the polarized relay 106 and of the relays 107, 108. On the first local subscriber A' hanging up, relays 101, 102, 103 de-energize, but the bridge across the conductors 141, 142 is still held at armature 130. Relay 109 then energizes and locks up over armature 115 and ground G<2>, and releases the incoming connector D, breaking the holding circuits of the switching relay 20.and ring cut-off relay 17, and completing a circuit G<6>, 136, 125, 49 for the release magnet 23. Should the subscriber A<2> desire to transfer the call to a third subscriber, on dialling the preliminary digit 1, the back-bridge relay 200 is momentarily deenergized and reverses the current through the polarized relay 106, which relapses and de-energizes relay 107, thereby energizing relay 105, which prepares a circuit 126, 127, 51 for relay 104, which is closed an instant later when relay 107 again pulls up. Relay 104 prepares an operating circuit G<6>, 118, 128, 131, 122, 50 for the connector D, subsequent closures of this circuit at the armature 128 being brought about by the dialling impulses, which cause the intermittent relapse of relays 200, 106, 107. The wipers of the incoming connector D having been brought into engagement with the wanted party in known manner, when this party answers, relays 101, 102 respond and the relay 109 is de-energized. The transferring subscriber A<2> may now enter into a three-cornered conversation, or by hanging up he may release the connection over the local connector H and the line switch C. In this case the de-energization of the back bridge relay 200 causes the relapse in turn of relays 106, 107, 104, 105, 108, and the bridge across conductors 141, 142 is broken, releasing the local connector H and line switch C as previously described. The remaining local subscriber may again transfer the call over the local connector H if desired. Final release may be effected at any time by the main exchange subscriber hanging up. If the incoming connector D is in operated position, the relapse of relays 14, 15, will energize the release relay 23, whilst if a local connector H is in use, relapse of relays 108, 109, consequent upon the disconnection of ground G<2>, will break the bridge across the conductors 141, 142 and initiate its release. Second method, Figs. 3 and 4. A main exchange subscriber is connected in known manner to a P.B.X. subscriber A over an incoming selector E<3>, Fig. 3, and an incoming connector H<3>, Fig. 4. The incoming selectors are provided with additional vertical and rotary test wipers, 334, 333, respectively, engaging additional vertical and rotary test banks. All the contact banks of each incoming selector E<3> and multipled locally in corresponding banks of an associated finder switch J, which is a Strowger-type switch provided with additional vertical and rotary test wipers 463, 462 similar to those of the selector E<3>. The vertical test wipers may conveniently be attached to the cup spring cases of the switches. When the selector E<3> engages an idle connector H<@3>, relays 311, 312, Fig. 3, energize in series with the line relay 395, Fig. 4, the relay 311, however, failing to respond in this circuit, its lower winding being differentially energized over a local circuit G<1>, 446, 340. On the called party A answering, the back-bridge relay 390 energizes a series relay 393 which reverses the current over conductors 336, 338 causing the response of the differential relay 311 and the application of earth at G<10> to the test wipers 333, 334. If, after connection has been established, the subscriber A wishes to transfer the call, he dials the prefatory digit 1, thereby momentarily de-energizing the back-bridge relay 390 and energizing a relay 397, which locks up and disconnects battery from